This invention relates to an improved monitor for double safety valves and more particularly to an improved and simplified device for indicating malfunctions.
In order to provide improved safety for pneumatically operated tools such as stamping presses or the like, it has been proposed to provide a double valve assembly between the pressure inlet and the supply port to the pneumatically operated device. With such arrangements, supply pressure is not supplied to the device from the inlet unless both of the valve elements are in an opened position. With such an arrangement, malfunction of one valve element will not permit pressure to be applied to the press nor will it permit actuation of the device. Examples of valves of this type are shown in the following U.S. Pat. Nos. 3,670,767, issued June 20, 1972, reissued on Aug. 19, 1975 under U.S. Pat. No. 28,520 and subsequently reissued on Mar. 1, 1983 under U.S. Pat. Nos. 31,161; 3,757,818, issued Sept. 11, 1973; 3,858,606, issued Jan. 7, 1975; and U.S. Pat. No. 4,257,455, issued Mar. 24, 1981.
In connection with this type of valve, it is also proposed to provide some form of monitoring device that will indicate if one of the valve elements is stuck in a faulted condition. Such a monitoring device will warn the operator if there is a fault condition. In one form of monitor, as shown in aforenoted U.S. Pat. No. 4,257,455, a shuttle valve is provided that is responsive to downstream pressure of the individual valve elements so that if one valve element is pressurized on its downstream side and the other is not, a malfunction signal will be indicated. Such arrangements have particular utility because they permit accurate monitoring of the function of both valve elements. However, such arrangements are complicated and add to the complexity of the valving arrangement.
In another form of monitoring device, a pressure sensing switch is provided in the supply port that provides the output to the device being operated and a restriction is provided in the exhaust port, normally by means of a restricted muffler. Hence, if one of the valve members is stuck in an opened condition, a leakage output pressure will be generated that can provide a malfunction signal. However, such devices require the use of restrictions in the exhaust port and thus can adversely affect the performance of the associated equipment.
It is, therefore, a principal object of this invention to provide an improved and simplified monitor for double valve assemblies.
It is another object of this invention to provide an improved, simplified and low cost device that provides an arrangement for monitoring defects in double valve assemblies to indicate a fault condition under all circumstances.